The present invention relates to a means for isolating and protecting the mechanical components of a fan drive from the circulating air or gas stream in a thermal processing chamber such as a dryer, freezer, bread proofer or the like.
Fans are frequently used to move air or other gases that are either heated or cooled relative to ambient conditions. In such case it is advantageous to isolate the motor and associated components which drive the fan from the stream of the driven gas. In this way, the fan drive motor and associated components are not subjected to the heated or cooled driven air and their life is thus extended. In some applications, such as food drying, it is also advantageous to prevent the contamination of the circulating air by oil or other potentially contaminating materials associated with the motor or fan drive means. For example, if a fan is being used to drive heated air through ductwork, it is common practice to mount the motor which propels the fan on the exterior of the ductwork adjacent to the fan and using a drive belt or other fan drive means to propel the fan on the interior of the ductwork and thus move the heated air.
In some circumstances, however, this type of arrangement is not entirely satisfactory. For example, if the heated air is intended to be used in the drying of food or food products, then complete cleaning of all interior surfaces of the ductwork and fan mechanism are required periodically. However, because the fan motor is mounted on the exterior surface of the ductwork adjacent to the fan, such surface must be a permanently fixed surface and cannot be easily removed for cleaning purposes. A further problem of this arrangement is that even though the fan drive motor is located outside of the air stream, the fan drive means are located inside the air stream and even if isolated from the air stream by an enclosure, such enclosure becomes heated because there is generally very poor air circulation within such enclosures.
In accord with the present invention, a new fan drive means enclosure has now been developed to overcome the above-identified disadvantages of the prior art enclosures. The present enclosure allows for the mounting of the fan drive motor in an out-of-the-way location, isolates the fan drive means from the fan driven air and provides a simple and efficient means of circulating cooling air through the enclosure. This is accomplished by providing two or more opening means from the enclosure to the exterior of the ductwork or chamber. In a preferred embodiment of the present invention the opening means are located in the top and the bottom of the ductwork or chamber thereby taking maximum advantage of the "chimney effect" created by slightly warmed air rising within the fan drive means enclosure which provides a natural form of air circulation therein by convection.